Most conventional carpets comprise a primary backing with yarn tufts in the form of cut or uncut loops extending upwardly from the backing to form a pile surface. In the case of tufted carpets, the yarn is inserted into a primary backing by tufting needles and a binder (carpet coating) is applied thereto. In the case of non-tufted or bonded pile carpets, the fibers are embedded and actually held in place by the binder composition.
In both cases, the carpet construction usually also includes a secondary backing bonded to the primary backing. The secondary backing provides extra padding to the carpet, absorbs noise, adds dimensional stability and often functions as a heat insulator. The secondary backing, typically either a woven fabric such as jute or a foam sheet, is laminated to the primary backing by a binder composition (carpet coating) applied to the tuft-lock coated primary backing. Similar techniques are used in the preparation of continuous (rolled) carpets as well as carpet tiles.
Generally these applications require a high degree of water resistance. In addition, there are a number of important requirements which must be met by such a carpet coating. It must be capable of being applied to the carpet and dried using the processes and equipment conventionally employed in the carpet industry for emulsion coating. It must provide excellent adhesion to the pile fibers to secure them firmly to the backing, both in tufted and non-tufted constructions. The coating also must have low smoke density values and high flame retardant properties and must accept a high loading with fillers such as calcium carbonate, clay, aluminum trihydrate, barite, coal fly ash and feldspar. Furthermore, the coating must maintain sufficient softness and flexibility, even with high filler loading or at low temperature, to enable the carpet, if prepared in continuous form, to be easily rolled and unrolled during installation.
WO 90/00967 A1 describes the use of an aqueous polymer latex instead of PVC plastisol for the manufacturing of carpets. Examples of such aqueous latices are vinyl acetate-ethylene copolymers, styrene-butadiene copolymers, and styrene-acrylate copolymers.
U.S. Pat. No. 3,779,799 describes a tuft pile fabric which is coated with aqueous polymer latices based on a vinyl acetate-ethylene copolymer, polyethylene or a carboxylated styrene-butadiene copolymer. In a primary backing woven from synthetic yarns for tufted fabrics and other products, such as carpet and the like, an enhancement in the carpet and/or tufted fabrics tuft raveling resistance capabilities is said to be obtained when the backing is coated with a polymeric substance which effectively reduces such tuft raveling to an acceptable degree. The preferred coating material is a copolymer of ethylene vinyl acetate, and is applied to the backing by any known method including spraying, immersing, brushing or rolling.
U.S. Pat. No. 5,026,765 discloses a carpet coating composition comprising 40 to 80 percent by weight filler and 20 to 60 percent by weight of a latex binder, the binder comprising an emulsion polymer of a) 40 to 80 wt % of a vinyl ester of an alkanoic acid, the acid having from 1 to 13 carbon atoms; b) 5 to 25 wt % of a copolymerizable comonomer having a Tg of at least 50° C.; and; c) 10 to 30% ethylene.
U.S. Pat. No. 4,239,563 discloses use of vinyl acetate-ethylene copolymer emulsions as laminating adhesives for rug backing. The copolymer emulsions are prepared by admixing vinyl acetate-ethylene copolymer, dispersant and thickening agent together, with or without the addition of filler. The vinyl acetate-ethylene copolymer can contain between about 20 and about 70 parts by weight of vinyl acetate and between about 30 and about 80 parts by weight of ethylene. The resulting vinyl acetate-ethylene copolymer emulsions have a glass transition temperature (Tg) of between about −35° C. and about −10° C. The copolymer dispersion is prepared with or without emulsifier. When polyvinyl alcohol is employed as a protective colloid, it is not necessary to add an emulsifier.
WO 2010/089142 discloses vinyl acetate-ethylene-copolymer dispersions suitable in particular for treating textile web materials, and textile web material treated therewith, being suitable in particular as floor coverings or as belts. The vinyl acetate-ethylene-copolymer dispersions are characterized by a low ethylene unit content, relatively high glass transition temperatures, and a small particle size. The vinyl acetate-ethylene copolymer comprises 1 to 4 wt % of ethylene, stabilized with anionic and/or nonionic emulsifier, optionally in the presence of protective colloids. The present inventors have found, however, that the carpet coating composition is too stiff, because of the low content of ethylene in the copolymer, and that the amount of polyvinyl alcohol used in the composition is too low, which negatively impacts dispersion stability and dry and wet tuft bind strength.
US 2005/0287336 A1 is directed to carpet coating compositions employing an emulsion binder prepared by emulsion polymerization of ethylene, a vinyl ester monomer and a functional monomer, and to carpet products prepared with these compositions. The compositions are said to have improved adhesion to polyvinyl butyral backings. The copolymer in the emulsion comprises 60 to 80 wt % of vinyl acetate, 20 to 40 wt % of ethylene, and 1 to 10 wt % of functional comonomers such as those comprising carboxyl groups, amide groups, N-methylol amide groups or hydroxyalkyl groups. The Tg values of the copolymers are at or far below 0° C. The present inventors have found that such binders are too soft, resulting in insufficient tuft bind and delamination strength.
Carpet binders may comprise carpet coating compositions based on crosslinkable copolymers so as to obtain a high degree of water resistance. For example, U.S. Pat. No. 6,359,076 B1 describes a carpet back coating composition based on a vinyl acetate-ethylene copolymer that includes OH-functional monomer units, which copolymer is combined with a crosslinking agent.
GB patent 1298155 describes a process for the production of a foam-backed tufted carpet wherein a latex of vinyl acetate-ethylene copolymer is used in combination with a crosslinking component based on polyvinyl alcohol and glyoxal.
WO 2011/139267 A1 and WO2011/140065 A2 both describe carpet binders based on vinyl acetate-ethylene copolymer latices with crosslinkable monomer units. For crosslinking, silane comonomer units or multifunctional comonomers capable of crosslinking with dihydrazide crosslinkers are introduced into the copolymer. The carpet binders should be substantially free of polyvinyl alcohol for obtaining compatibility with other carpet binders such as styrene-butadiene emulsions.
Crosslinkable carpet binders such as discussed above have the disadvantage of being too dimensionally stable and having a memory effect. Thus, when the carpet is stretched during installation, there is a tendency for the carpet to return to its original dimensions. This results in buckling of the carpet, requiring effort by the installers to remove it. In addition, such crosslinkable binders tend to cause embrittlement, and some crosslinkable comonomers, particularly silane-functional monomers, have the disadvantage of releasing volatile organic compounds (VOC) during crosslinking. A further disadvantage is the high costs of such copolymers with expensive crosslinking comonomers.
In some adhesive applications, emulsions of vinyl acetate-ethylene copolymers may be stabilized with a combination of protective colloids and emulsifiers. For example, EP 385734 A2 discloses an adhesive with high setting speed based on a vinyl acetate-ethylene copolymer emulsion stabilized with a mixture of low-molecular weight, partially saponified polyvinyl alcohol and a polyoxyethylene nonionic surfactant having an HLB value of 16.5 to 17.5.
WO 99/10396 A1 discloses a high solids vinyl acetate-ethylene copolymer emulsion comprising a low-molecular weight polyvinyl alcohol, an ethoxylated aliphatic surfactant, and a dispersant.
U.S. Pat. No. 5,124,394 describes high solids vinyl acetate-ethylene copolymer emulsion, among others, for use in carpet manufacture. Polyvinyl alcohol is removed and substituted by poly(ethyloxazoline) for the improvement of adhesion properties.
U.S. Pat. No. 4,921,898 describes vinyl acetate-ethylene copolymers prepared in the presence of a low viscosity polyvinyl alcohol and a surfactant.
US patent application 2008/0039572 discloses an aqueous vinyl ester-ethylene copolymer dispersion useful as an adhesive for nozzle application processes. The vinyl ester copolymer dispersion is stabilized with a combination of at least one emulsifier and at least one protective colloid, such as a high-viscosity polyvinyl alcohol.
U.S. Pat. No. 4,735,986 and U.S. Pat. No. 5,084,503 describe a vinyl acetate-ethylene copolymer emulsion comprising an aqueous colloidal dispersion of a copolymer containing 65 to 90 wt % vinyl acetate and 10 to 35 wt % ethylene prepared by the emulsion polymerization of the monomers in the presence of a stabilizing system consisting essentially of an 86 to 90 mole % partially hydrolyzed polyvinyl alcohol, a 98 to 99+ mole % fully hydrolyzed polyvinyl alcohol, in a partially hydrolyzed polyvinyl alcohol:fully hydrolyzed polyvinyl alcohol weight ratio from 3:1 to 1:3, and a nonionic polyalkoxylated surfactant. Also disclosed is a carpet backing adhesive composition comprising such a vinyl acetate-ethylene copolymer emulsion, about 0.1 to 3 parts by weight dispersant, about 0.1 to 10 parts by weight thickening agent and between 300 and about 1000 parts by weight filler, all of the components being per 100 parts of the copolymer.
WO/2012/020319 discloses carpet products comprising at least one flexible substrate and at least one coating and/or adhesive layer associated with the at least one flexible substrate. The coating and/or adhesive layer is formed from an aqueous composition comprising: A) an emulsifier-stabilized vinyl acetate/ethylene (VAE) emulsion copolymer dispersion wherein the VAE copolymer therein comprises co-monomers which include at least vinyl acetate copolymerized with ethylene and optionally also with other additional functional and/or non-functional co-monomers; and B) at least one particulate filler material selected from particulate inorganic compounds and particulate plastic material. The vinyl acetate/ethylene copolymer in the copolymer dispersion has a selected ethylene content or glass transition temperature.
WO/2012/020321 discloses carpet products comprising at least one flexible substrate and at least one coating layer associated with the at least one flexible substrate. The coating layer is formed from an aqueous composition comprising: A) an emulsifier-stabilized vinyl acetate/ethylene (VAE) emulsion copolymer dispersion wherein the VAE copolymer therein comprises co-monomers which include at least vinyl acetate copolymerized with ethylene and optionally also with other additional functional and/or non-functional co-monomers; and B) at least one particulate filler material selected from particulate inorganic compounds and particulate plastic material. The vinyl acetate/ethylene copolymer in the copolymer dispersion has a particle size, dw, ranging from about 50 to about 500 nm as determined by Laser Aerosol Spectroscopy. The carpet products are said to maintain their integrity and appearance after multiple machine washing operations. Despite the above-mentioned efforts, certain properties of VAE-based carpet coating compositions would benefit from further advances. In particular, VAE-based compositions may not provide high levels of wet performance, such as wet tuft bind strength and wet delamination strength. Further, conventional VAE-based carpet compositions may require the inclusion of significant amounts of thickeners, which tend to be relatively expensive. For these and other reasons, improved VAE-based carpet coating compositions would be of significant commercial interest.